Diisocyanate is an organic compound having two isocyanate groups (—NCO), and is widely used industrially as a material for, for example, polyurethane and polyurea.
Conventionally, diisocyanate has been industrially produced by reaction (phosgene method) between amine and phosgene. However, phosgene has various problems such as being highly toxic and troublesome in handling, and requiring careful attention to corrosion of the equipment because it by-produces a large amount of hydrochloric acid. Accordingly, there is a need to develop industrial production methods for isocyanate that can replace the phosgene method.
Known diisocyanate production methods that do not use phosgene include a method (urea method) in which diamine, urea, and/or N-unsubstituted carbamic acid ester, and alcohol are allowed to react (carbamate-forming reaction), and the obtained N-unsubstituted carbamic acid ester (carbamate) is thermally decomposed to produce diisocyanate.
To be specific, for example, Patent Document 1 below has proposed a method for producing alicyclic diisocyanate in which, for example, alicyclic diamine, alcohol, and urea and/or urea derivative are allowed to react to synthesize diurethane; thereafter, the low boiling material, medium boiling material, and high boiling material are removed from the obtained diurethane, and furthermore, the alicyclic diurethane is thermally decomposed, and thereafter, alicyclic diisocyanate is separated, while reurethanzing a portion of the decomposed column bottom liquid with alcohol, recycling the reurethaniation product into the low boiling material separation.